Modified polypropylene resins

ABSTRACT

The present invention relates to polypropylene resin compositions comprising a syndiotactic polypropylene incorporating at least one particulate material or chemical additive.

The present invention relates to modified polymer resins that can beused either alone or in dust-free master-batches.

It is known in the art that the properties of a polymer may be modifiedby introducing particulate material or chemical additives into thepolymer resin matrix in order to produce a composite material. Theparticulate material or chemical additive is selected depending on thedesired properties of the composite material. Particulate materials aretypically introduced into polymer resins for increasing the mechanicalproperties of the resin, for example the rigidity or wear resistance,the thermal properties and/or the electrical properties, or they areintroduced to confer new functionalities to the polymers such as forexample flame retardant or anti-microbial properties.

For example, JP-A-60-023432 discloses a composite resin compositioncomposed of polypropylene, mica treated with an organosilane compound,modified polyolefin and glass fibre treated with an organosilanecompound. The composition is stated to have high rigidity and excellentfluidity, shrinkage anisotropy and retention of flexural strength at aweld part.

JP-A-02-173048 discloses a polyolefin resin composition incorporating aninorganic filler, such as precipitated calcium carbonate, for improvingthe impact strength without impairing the rigidity of the composition.

JP-A-60-020947 discloses a resin composition for use in the productionof packaging boxes consisting of polypropylene, high densitypolyethylene, an inorganic filler such as calcium carbonate and amodified polyolefin. The resultant composition is stated to haveimproved properties such as an excellent hinge at a fold, embossingcharacteristics, printability, adhesion and water resistance.

JP-58-040602 discloses a resin composition for an acoustic materialcomposed of polypropylene, an inorganic filler such as calcium carbonateor talc, polyethylene and a modified polyolefin. The compositionexhibits high impact strength, flowability and good acoustic properties.

When particulate fillers are incorporated into polypropylene which hasbeen produced using a Ziegler-Natta catalyst (hereinafter Ziegler-Naftapolypropylene (znPP)) or a metallocene catalyst (hereinafter metallocenepolypropylene (mPP)), for example by compounding the polypropylene andthe particles added thereto in an extruder or in a Brandburry malaxor,there tends to be an undesired dramatic increase in brittlenessaccompanying the increase in the concentration of the particulatematerial.

The present invention aims to provide polymer resin compositionsincorporating particulate materials or chemical additives, said resinshaving improved properties.

Accordingly, the present invention provides a polymer resin comprisingsyndiotactic polypropylene (sPP) incorporating at least one particulatematerial or chemical additive.

The present invention is predicated on the discovery by the presentinventor that with syndiotactic polypropylene (sPP) a much higherconcentration of particles in the resin can be achieved compared toznPP, yet with the composite material tending to retain a higherflexibility and impact resistance compared to the correspondingproperties obtainable with a particulate material incorporated intoznPP.

The syndiotactic polypropylene is preferably a homopolymer or a randomcopolymer with a rrrr of at least 70%. The sPP may alternatively be ablock copolymer having a higher comonomer content, or a terpolymer.Preferably, the sPP has a melting temperature of up to 160° C. andtypically, it has two melting peaks, the positions of which depend uponthe percentage of racemic pentad in the sPP. The sPP has a melt flowindex MI2 of from 0.1 to 1000 g/10 min, preferably of from 1 to 60 g/10min. The MI2 is measured following the method of standard test ASTM D1238 at a temperature of 230° C. and under a load of 2.16 kg. The sPPmay have a monomodal or a multimodal molecular weight distribution, andmore preferably it has a bimodal molecular weight distribution in orderto improve the processability. The molecular weight distribution isdefined by the dispersion index D that is the ratio D=Mw/Mn of theweight average molecular weight Mw to the number average molecularweight Mn.

The filled sPP can be used in blends with a metallocene-producedpolyethylene (mPE) and/or a linear low density polyethylene (LLDPE)prepared by any known method in the art and/or a polypropylene preparedwith a Ziegler-Natta catalyst (znPP) or prepared with a metallocenecatalyst (mPP). The blend comprises more than 20 wt % of sPP, based onthe total weight of the polymers in the blend.

In one preferred aspect of the invention, the particles are incorporatedinto the sPP in order to improve mechanical properties such as wearresistance. The particulate material may comprise at least one ofalumina, chopped glass fibres, chopped carbon fibres, calcium carbonate,carbon black, silicon beads or particles, graphite or nanoparticles. Theincorporation of these particulate materials into syndiotacticpolypropylene enables a much higher particulate concentration to beachieved as compared to znPP, yet retaining a very good impactresistance and flexibility, thereby allowing manipulation of thecomposite material without breaking it. Such sPP resins having improvedwear resistance may be used for technical parts or floor coverings.

In accordance with another aspect of the invention, the electricalconductivity of the syndiotactic polypropylene may be improved by theincorporation of electrically conductive particles as a filler into thesyndiotactic polypropylene. The electrically conductive particles maycomprise at least one of carbon black, carbon fibres, metallicparticles, or particles coated with electrically conductive material.

The electrical conductivity of the composite material depends upon theconcentration of the filler particles in the syndiotactic polypropylene.At low filler concentrations, the filler particles form clusters whereinthe particles touch each other but the clusters are individual andseparated from each other. With such a concentration range and suchmorphology, the composite is considered to be an electrically insulativematerial. However, the electrical conductivity generally increases withincreasing filler concentration. Accordingly, the use of electricallyconductive particles as a filler permits the manufacture of a compositehaving improved static electricity dissipation as compared to puresyndiotactic polypropylene.

With a yet further increase in the filler concentration, the particulateclusters start to touch each other, thereby forming an electricallyconductive body in the polymer matrix. In a very narrow range ofincreasing particulate concentration, the electrical resistivity of thecomposite suddenly drops, and the material becomes electricallyconductive. Such a concentration range is known as the “percolationthreshold”. Above the percolation threshold, any further increase in thefiller concentration results in a further increase of the electricalconductivity.

The concentration value at the percolation threshold depends on the typeand geometry of the filler particles. For elongate filler particles, thehigher the aspect ratio (or the shape factor defined as the ratio of thelargest to the smallest characteristic dimensions: for a fibre, theshape ratio is L/D, the ratio of length to diameter) of the particles,the smaller the value of the concentration at the percolation threshold.For carbon black particles, the more spherical the particles, the higherthe percolation threshold. In contrast, highly structured carbon blackparticles, i.e. particles of a complex shape, usually made from spheresmerged into each other, provide composites with a much lower percolationthreshold.

Composite materials having improved electrical conductivity have avariety of different applications. For example, syndiotacticpolypropylene when filled with particles such as carbon black or otherelectrically conductive materials can produce sPP having improved staticelectricity dissipation (i.e. low static electricity sPP), and may beused in applications requiring dissipation of static charges such as infibres for carpets, materials for avoiding dust accumulation, and theshielding or housing of electric or electronic components. Compositematerials having improved electrical conductivity also have applicationas electromagnetic shielding materials, for example for housing ofelectronic components, in mobile telephones, televisions or radios, ifthe concentration of the electrically conductive filler is around orabove the percolation threshold.

In a further aspect of the invention, the thermal conductivity ofsyndiotactic polypropylene is improved by the incorporation into the sPPmatrix of at least one thermally conductive filler, such as carbonfibres, carbon black, graphite particles, metallic particles or aluminaparticles. As for improving the electrical conductivity, the thermalconductivity also has a percolation threshold concentration for theincrease in thermal conductivity but the increase in thermalconductivity at the percolation threshold is much less pronounced thanfor electrical conductivity. Composite resins having improved thermalconductivity have applications as heat sinks for thermal management, orelectronic device housings.

The syndiotactic polypropylene composites in accordance with theinvention are preferably prepared by adding the particulate material orchemical additives to the syndiotactic polypropylene by blending orcompounding the materials together in an extruder or Brandburry malaxor.Alternatively, the syndiotactic polypropylene may be dissolved into asolvent, such as for example xylene and the particulate material can bedispersed in the solution. Thereafter the solvent is removed byfiltration, sublimation or evaporation to produce the compositematerial.

In a yet further alternative method, the syndiotactic polypropylene,which may be in the form of powder, pellets or fibres, may be dispersedin water or any other liquid in which the particulate filler is alsodispersed. Thereafter, the liquid is flushed away, in leaving anintimate blend of syndiotactic polypropylene and filler. This mixturecan be hot pressed or laminated and then further ground or re-extruded.This preparation technique has a particular application for themanufacture of composite materials where the particulate materialexhibits a high aspect ratio, which is to be preserved in the ultimatecomposite material.

The maximum filler concentration depends both on the nature andcomposition of the polymer and of the particulate material, inparticular the geometry of the particulate material. For particulatematerials having a large aspect ratio, as a rule the maximumconcentration of particulate material in the polymer is low. With regardto the percolation threshold, as soon as the percolation thresholdconcentration is obtained, the rigidity and brittleness of the compositetends to increase dramatically. For composite materials prepared usingexactly the same conditions with identical fillers, the percolationthreshold tends to be slightly higher with syndiotactic polypropylene ascompared to Ziegler-Natta polypropylene. Furthermore, the use ofsyndiotactic polypropylene as compared to Ziegler-Natta polypropylenetends to result in a more flexible composite material which alsoexhibits a very good impact resistance, even above the percolationthreshold concentration.

The sPP has several other advantages such as transparency that makes ituseful for intermediate layers in packaging with changing light effectand such as adequate temperature range for colorants that makes ituseful for black parts in the automotive market.

EXAMPLES

The syndiotactic polypropylene was produced with acyclopentadienyl-fluorenyl metallocene catalyst and had a melt flowindex MI2 of 3.6 g/10 min as measured following the method of standardtest ASTM D 1238 at a temperature of 230° C. and under a load of 2.16kg. It had two melting peaks respectively at 110 and at 127° C., anumber average molecular weight (Mn) of 37426, a weight averagemolecular weight (Mw) of 160229 and a molecular weight distribution of4.3. The molecular weight distribution is defined here by the dispersionindex (D) that is the ratio Mw/Mn. The density was 0.89 g/cm³, asmeasured at 23° C. following the method of standard test ASTM D 1505.

It has been blended respectively:

-   -   with the anti-microbial Irgaguard B 1000 from CIBA in order to        produce various woven or non-woven materials used for example in        hygiene;    -   with the anti-algae Irgaguard A 2000 from CIBA in order to        produce fibres used in medical, agricultural or marine        applications;    -   with the anti-static Irgastat P22 from CIBA in order to control        the static electricity in fabrics or in carpets;    -   with the flame retardant Flamestab NOR 116 from CIBA in order to        prepare woven or non-woven material used for example in        upholstery, carpets, carpet backings, professional and ordinary        clothing;    -   with of the anti-UV Tinuvin 783 from CIBA, that is a synergistic        mixture of chimassorb 944 and Tinuvin 622 or with 1 to 10 wt %        of chimassorb 2020 from CIBA in order to prepare material for        use in the textile industry;    -   with fillers such as kaolin or metal powders in order to        increase the density of the fiber above 1 g/cm³ for use in the        paper industry. In addition, the sPP will improve the rigidity        of the finished product. More generally, the filler can be a        weight additive that increases the density of the composition        above that of the reference immersing fluid.    -   with carbon black in order to improve the anti-static properties        of the woven or non-woven material.

Several types of “black” additives have been tested in order to increasethe electrical conductivity of polyolefin material. FIG. 1 representsthe electrical resistivity expressed in ohm.cm as a function of theconcentration of the “black” additive expressed in wt %. It is observedthat in all cases, the resistivity decreases rapidly as a function ofincreasing concentration of the “black” additive past a threshold thatis a function of the nature of the additive. For additives made ofnearly spherical particles such as furnace black, the threshold is veryhigh and concentrations of 25 to 50 wt % of additive in the sPP arenecessary to observe a decrease in resistivity. For additives havinghighly structured particles such as the product sold by MMM under thename Ensaco 350, the threshold is very low and concentrations of 9 to 15wt % of additive in the sPP are necessary to observe a decrease inresistivity.

The impact test performed on the filled sPP give good to outstandingresults depending upon the nature and the amount of the fillers used.

The filled sPP according to the present invention can either be usedalone as a master batch or it can be blended with one or more polymersselected from znPP, mPE or LLDPE.

1. A polymer composition comprising: A polymer component consistingessentially of: a first polymer, wherein the first polymer is acrystalline polymer selected from polypropylene resins prepared with aZiegler-Natta catalyst, polypropylene resins prepared with a metallocenecatalyst, polyethylene resins and combinations thereof; and at least 20wt. % of a second polymer, wherein the second polymer comprises asyndiotactic propylene polymer incorporating at least one filleradditive, the filler additive selected from particulate material,chemical additives and combinations thereof; and wherein the polymercomposition has a characteristic of at least one of flexibility andimpact resistance which is higher than the corresponding characteristicexhibited by the first polymer incorporating the filler additive withoutthe presence of the second polymer.
 2. The polymer composition of claim1, wherein said first polymer comprises a metallocene-producedpolyethylene or a linear low-density polyethylene.
 3. The polymercomposition of claim 2 wherein said first polymer is a linear lowdensity polypropylene.
 4. The polymer composition of claim 1, whereinsaid first polymer component comprises a polypropylene prepared with aZiegler-Natta catalyst or prepared with a metallocene catalyst.
 5. Thepolymer composition of claim 1, wherein said syndiotactic propylenepolymer has a racemic pentad content of at least 70%.
 6. The polymercomposition of claim 5 wherein said syndiotactic propylene polymer has abimodal molecular weight distribution.
 7. The polymer composition ofclaim 1, wherein said filler additive is a particulate material.
 8. Thepolymer composition of claim 7 wherein said particulate material isselected from the group consisting of glass fibers, carbon fibers,alumina particles, calcium carbonate particles, carbon black particles,silicon particles, graphite particles and mixtures thereof.
 9. Thepolymer composition of claim 7 wherein said particulate materialcomprises electrically conductive particles in a concentration at leastas great as the percolation threshold for electrical conductivity. 10.The polymer composition of claim 7 wherein said particulate materialcomprises heat conductive particles in a concentration at least as greatas the percolated threshold for thermal conductivity.
 11. The polymercomposition of claim 7 wherein said particulate material is ananti-microbial additive.
 12. The polymer composition of claim 7 whereinsaid particulate material is a flame retardant additive.
 13. The polymercomposition of claim 7 wherein said particulate material is ananti-static additive.
 14. The polymer composition of claim 7 whereinsaid particulate material is an anti-UV additive.
 15. The polymercomposition of claim 7 wherein said particulate material is a weightadditive having a density greater than the density of said polymercomposition.
 16. The polymer composition of claim 7 wherein theparticulate material is an anti-algae additive.
 17. The polymercomposition of claim 7 wherein the particulate material is a carbonblack additive.
 18. The polymer composition of claim 7 wherein theparticulate material is a carbon fiber additive.
 19. The polymercomposition of claim 7 wherein the particulate material is a mineralfiller.
 20. The polymer composition of claim 7 wherein the particulatematerial is a fungicide.